Some physicochemical factors influencing foliar uptake enhancement of glyphosatemono(isopropylammonium) by polyoxyethylene surfactants

Abstract

Structure‐concentration–foliar uptake enhancement relationships between commercial polyoxyethylene primary aliphatic alcohol (A), nonylphenol (NP), primary aliphatic amine (AM) surfactants and the herbicide glyphosatemono(isopropylammonium) were studied in experiments with wheat (Triticum aestivum L.) and field bean (Vicia faba L.) plants growing under controlled‐environment conditions. Candidate surfactants had mean molar ethylene oxide (EO) contents ranging from 5 to 20 and were added at concentrations varying from 0·2 to 10 g litre−‐1 to [14C]glyphosate formulations in acetone–water. Rates and total amounts of herbicide uptake from c. 0·2–μl droplet applications of formulations to leaves were influenced by surfactant EO content, surfactant hydrophobe composition, surfactant concentration, glyphosate concentration and plant species, in a complex manner. Surfactant effects were most pronounced at 0·5 g acid equivalent (a.e.) glyphosate litre−‐1 where, for both target species, surfactants of high EO content (15–20) were most effective at enhancing herbicide uptake: surfactants of lower EO content (5–10) frequently reduced, or failed to improve, glyphosate absorption. Whereas, at optimal EO content, AM surfactants caused greatest uptake enhancement on wheat, A surfactants gave the best overall performance on field bean; NP surfactants were generally the least efficient class of adjuvants on both species. Threshold concentrations of surfactants needed to increase glyphosate uptake were much higher in field bean than wheat (c. 2 g litre−‐1 and < 1 g litre−‐1, respectively); less herbicide was taken up by both species at high AM surfactant concentrations. At 5 and 10 g a.e. glyphosate litre−‐1, there were substantial increases in herbicide absorption and surfactant addition could cause effects on uptake that were different from those observed at lower herbicide doses. In particular, the influence of EO content on glyphosate uptake was now much less marked in both species, especially with AM surfactants. The fundamental importance of glyphosate concentration for its uptake was further emphasised by experiments using formulations with constant a.i./surfactant weight ratios. Any increased foliar penetration resulting from inclusion of surfactants in 0·5 g litre−‐1 [14C]glyphosate formulations gave concomitant increases in the amounts of radiolabel that were translocated away from the site of application. At these low herbicide doses, translocation of absorbed [14C]glyphosate in wheat was c. twice that in field bean; surfactant addition to the formulation did not increase the proportion transported in wheat but substantially enhanced it in field bean.

Herbicidas inibidores da EPSPs: revisão de literatura

“…Estes produtos aumentam a hidratação da cutícula, incrementando a difusão de glyphosate através da mesma (Sherrick et aI., 1986;Gaskin & Holloway, 1992;de Ruitner & Meinen, 1998).…”

Surfactant-Increased Glyphosate Uptake into Plasma Membrane Vesicles Isolated from Common Lambsquarters Leaves

“…Cationic polyoxyethylene tertiary amine surfactants are more effective than nonionic surfactants at promoting glyphosate phytotoxicity (Wyrill and Bumside, 1977;Riechers, 1992). Although several studies have examined surfactant mode of action in promoting glyphosate phytotoxicity (O'Donovan et al, 1985;Sherrick et al, 1986aSherrick et al, , 1986bde Ruiter et al, 1988;Gaskin and Holloway, 1992;Rdyneberg et al, 1992;Stock et al, 1992), the precise mechanism(s) of surfactant interaction has not been deduced. Surfactants promoting greatest glyphosate phytotoxicity are required at higher concentrations than necessary for maximum reduction of the spray solution surface tension, indicating that their mode of action is not limited to increasing the spreading characteristics of the spray droplet (Sherrick et al, 1986b).…”

Influence of two fatty amine surfactants on foliar absorption, translocation, and efficacy of 2,4-D triethanolamine salt

“…The critical log KO, range has been defined as the range in which surfactant lipophilicity (based on EO content) does not strongly influence the uptake enhancement of compounds; its upper and lower limits may vary according to plant species (Stock et al, 1993). The contribution of the nitrogen atom to the hydrophilicity of ethoxylated alkylamines need not weaken greatly the influence of EO content as indicated in a previous study (Gaskin and Holloway, 1992). These authors demonstrated that reducing of the EO content of ethoxylated alkylamines to 5 or 10 mol reduced the surfactant-induced uptake of the polar compound glyphosate by field bean and wheat.…”